The customer called because the rooftop air conditioner was not cooling. Fusion Heating & Cooling inspected the Trane/American Standard rooftop gas package unit in Loomis, CA and found the evaporator coil freezing. Ice was visible across sections of the coil, showing that the cooling system was not feeding the evaporator normally.
After troubleshooting the system, we found a refrigerant restriction at the metering pistons in the distributor manifold. This is an older R-22 unit. For this design and this diagnosed restriction, the planned repair is to remove the restricted piston manifold and install a model-matched TXV kit with the correct distributor assembly.
Diagnosing the Frozen Rooftop AC Unit
The ice in the photo was a symptom, not the complete diagnosis. Airflow and refrigerant conditions were checked before identifying the restriction. The frost pattern and system behavior pointed to restricted refrigerant flow through the metering pistons serving the evaporator circuits.
Because the pistons are part of the manifold arrangement, this repair is more involved than replacing a single accessible orifice. The restriction must be addressed at the refrigerant distributor and metering assembly.
Planned R-22 TXV and Distributor Conversion
The first step is to record the exact model, serial number, capacity, refrigerant, and existing metering configuration. A Trane/American Standard TXV kit must be approved for the specific unit and sized for its R-22 application. A kit number should never be selected from appearance alone.
Once the correct OEM components are obtained, the planned repair process includes:
- Shut down and electrically isolate the rooftop package unit.
- Recover the R-22 refrigerant before opening the sealed system.
- Access the evaporator metering assembly and protect the coil and distributor tubes from damage.
- Remove the restricted manifold and plugged piston metering components.
- Install the correct distributor assembly and R-22 thermostatic expansion valve.
- Connect the external equalizer where required by the kit.
- Secure the sensing bulb tightly to a clean section of the suction line in the position specified by the manufacturer, then insulate the bulb.
- Replace the liquid-line filter drier as part of opening and repairing the commissioned refrigerant circuit.
- Pressure-test the completed connections with dry nitrogen and check for leaks.
- Evacuate the system to the target in the approved service instructions, then recharge it using the unit data and manufacturer charging procedure.
- Start and test the unit after the coil is fully thawed, then verify airflow, refrigerant feeding, temperatures, and stable operation.
The exact fittings, torque values, bulb position, charge procedure, and kit components must come from the installation instructions for the matched TXV kit and rooftop unit. This project description documents the repair plan; it does not substitute for the unit-specific service literature.
Servicing an Existing R-22 System
R-22 equipment can still be serviced, including replacement of failed components. The U.S. EPA explains that newly produced and imported R-22 ended in 2020, while previously produced, recovered, recycled, or reclaimed R-22 may be used to service existing equipment.
R-22 must be recovered before the refrigerant circuit is opened and may not be knowingly vented. Learn more from the EPA guidance for technicians and contractors.
Why Adding Refrigerant Would Not Fix This Restriction
This diagnosis was not simply a low-charge condition. Adding refrigerant would not remove plugged metering pistons or correct restricted flow through the manifold. The refrigerant control assembly must be repaired, and the final charge must then be verified after the system is clean, sealed, evacuated, and operating.
Need Rooftop AC Repair in Loomis, CA?
A frozen coil can have several causes, so the repair should begin with a complete diagnosis. Fusion Heating & Cooling services rooftop package units and other residential and commercial HVAC systems in Loomis and nearby communities.
Call (916) 666-0074 or request service online for AC repair in Loomis, CA.
Frequently Asked Questions
What caused this rooftop AC unit to freeze?
Testing on this Loomis service call identified restricted metering pistons in the refrigerant distributor manifold. The restriction prevented the evaporator coil from being fed normally and produced the visible freezing pattern.
What is the planned repair?
The repair plan is to obtain the correct R-22 TXV kit for the exact unit, remove the restricted piston manifold, install the matched distributor and TXV assembly, pressure-test and evacuate the circuit, recharge it correctly, and verify system operation.
Can an existing R-22 air conditioner still be repaired?
Yes. EPA guidance allows existing R-22 equipment to be serviced and failed components to be replaced. Refrigerant recovery and other Section 608 service practices still apply.